Many methods of welding are known in the art, each with its own advantages and disadvantages. Common welding processes include gas welding, oxyacetylene brazing and soldering, shielded metal arc welding (SMAW) or "STICK" welding, metal inert gas (MIG) or "wire feed" welding, and gas tungsten arc welding (GTAW) or "TIG32" welding. MIG welding is notable for its simplicity and speed. Although the apparatus of the present invention is described with reference to a MIG welding power supply, one skilled in the art will appreciate that the present invention may have applications in many other welding power supplies.
MIG welding power supplies may operate in a short circuit transfer technique, a pulsed spray transfer technique, or a continuous spray transfer technique. In short circuit transfer, filler wire is automatically fed from the power supply to a welding site. A welding current is applied to the filler wire which generates a welding arc between the filler wire, acting as an electrode, and a workpiece. As the operator draws the electrode along the workpiece at a welding site, the filler wire creates a short circuit with the workpiece, releases a drop of filler wire thereby opening the circuit, and, subsequently, the filler wire is advanced to create another short circuit. Thus, the filler wire and the workpiece make a series of short circuit contacts as filler wire is applied to the workpiece. One disadvantage of the short circuit welding process on aluminum material is that the weld is porous (i.e., has a poor diffusion quality). On steel, short circuit welding works well and is an accepted standard method, but it should not be used on aluminum material due to the lack of fusion of the weld. Furthermore, the porosity of the short circuit transfer weld on aluminum causes a weaker weld. During short circuit welding, the arc gives off a characteristic, audible "sizzle" sound.
In a pulsed spray transfer welding technique, the filler wire does not create a short circuit with the workpiece. This is accomplished by the welding device creating a pulsed welding current, including a first lower welding current and a second higher welding current (and perhaps additional current levels). Because the pulsed spray operates at these different current levels, the filler wire creates a weld puddle that is allowed to freeze slightly between pulses. Also, the average current is maintained lower than that of continuous spray, while the peak amperage of the pulse is great enough to create an axially-stable arc. These features provide for better control of welding of thin metals. Preferably, at least one of the first lower welding current and second higher welding current is applied above a transition current of the filler wire. The transition current of the filler wire is the current at which the welding arc provides a sufficient magnetic field to direct the molten filler wire in the direction of the workpiece. This creates an axially-stable welding arc, since the magnetic field of the arc is capable of directing molten filler wire in all positions on the workpiece, including positions reachable only against the direction of gravity. Continuous spray welding does not require a pulsed welding current, but takes place at higher currents than does the short circuit transfer technique.
Many low-cost MIG welding power supplies only allow for short-circuit transfer or continuous spray transfer. Most power supplies which allow for pulsed spray transfer are significantly more expensive (e.g., inverter-based power supplies), in part because these power supplies also allow for operator control over the various characteristics of the welding pulse (e.g., pulse width, pulse frequency, pulse amplitude, etc.). Accordingly, the prior art fails to disclose a welding device capable of pulsed spray transfer to achieve a high-quality weld with a low welding current in a low-cost and easy to use welding device. Recently, the Aluminum Association has promoted the pulsed welding method for aluminum; however, a suitable low-cost and easy to use pulsed spray welding power supply is unavailable.
Since the Aluminum Association has endorsed pulsed spray welding for welding light-gage aluminum and other metals, less experienced welders are likely to find a need for a suitable low-cost welding device. Presently available pulsed spray welding devices contain a plurality of adjustment knobs, which allow an unskilled operator to select invalid or undesirable pulsed spray welding conditions. Such operators are accustomed to adjusting voltage and wire feed speed in short circuit or continuous spray power supplies, but are less familiar with the plurality of settings required for a suitable pulsed spray welding power.
Accordingly, what is needed is a pulsed spray welding device having simplified operator interface controls that are suitable for commonly used types of filler wire in common aluminum or other thin metal welding applications. Further what is needed is a welding power supply that has short circuit transfer, pulsed spray transfer and continuous spray transfer capabilities to allow an operator to utilize the advantages of continuous spray transfer (e.g., for such applications as aluminum or steel welding wherein the thickness of the aluminum or steel is great), pulsed spray transfer for thinner materials, and short-circuit transfer for thinner steel materials. This system also would be low-cost and easy to operate.